Production of etched patterns in a continuously moving metal strip



Dec. l0, 1968 s. A BROWN PRODUCTION 0F ETCHED PATTERNS IN A CONTINUOUSLY MOVING METAL STRIP Filed March 29, 1965 3 Sheets-Sheet 1 QN Ev FQ AN NN WM. WN

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Dec. 10, 1968 s. A` BROWN 3,415,699

PRODUCTION 0F ETCHED PATTERNS IN A CONTINUOUSLY MOVING METAL STRIP Filed March 29, 1965 3 Sheets-Sheet 2 INYFNTOR, 5ans .Baan/v rroflwfys Dean), 1968 S A4 BROWN 3,415,699

PRODUCTION OF ETCHD PATTERNS IN A CONTINUOUSLY MOVING METAL STRIP Filed March 29, 1965 l 5 Sheets-Sheet 3 INVENTOR. Su as A BRoA/v United States Patent 3,415,699 PRODUCTION F ETCHED PATTERNS IN A CONTINUOUSLY MOVING METAL STRIP Silas Arthur Brown, Lake Elmo, Minn., assignor to Buckbee-Mears Company, St. Paul, Minn., a corporation of Minnesota Filed Mar. 29, 1965, Ser. No. 443,338 7 Claims. (Cl. 156-13) ABSTRACT OF THE DISCLOSURE A strip of metal, such as stainless steel, is unwound from a supply reel and initially thoroughly cleaned then fed through a further processing area where it is coated with a light sensitive material or enamel. From there the strip is fed into a printing station where a predetermined pattern, which will be later etched out of the metal, is printed on the light sensitive coating. This is accomplished by placing a surface containing an opaque substance adjacent the coated metal strip while it is continuously moving and bringing the surface into momentary pressing contact with the coated surface to deposit the opaque substance on selected areas of the coating. The printed metal strip is then passed through an exposure chamber and 4a developing area where the unprotected enamel is hardened and the opaque substance with the underlying unhardened enamel is removed. Next the strip continues its travel into a etching chamber where the unprotected areas of the metal strip are chemically etched or milled. In this fashion the pattern to be etched out of the metal strip can be printed without the need for even momentarily interrupting the continuous ow of the metal strip. In the case of etching the metal strip through from both sides, the patterns are printed in register on opposite sides of the metal strip in the same fashion.

This invention relates generally to the etching of designs or patterns on metallic surfaces, and pertains more particularly to a method and apparatus for doing so on a continuous or uninterrupted basis.

Printed circuits are widely used, and a number of techniques have been developed for fabric-ating panels, boards and rolls of metallic stock with the required wiring pattern thereon. For Various reasons, etched circuits have met with considerable acceptance and it is with respect to patterns formed by etching that this invention is concerned. It will be understood that the invention is not limited to circuits as such, but that it can be utilized in conjunction with the fabrication of masks for television tubes,

commutators, components, windings, etc., as well as nonelectrical designs which include such patterns as hole layouts. For instance, the invention will find especial utility in the making of sieves and other perforated items where holes are to extend completely through the metal sheet or strip.

One object of the present invention is to provide a method and apparatus for making etched patterns which will be of a continuous character. In this regard, previous techniques have involved manufacturing steps that cannot be performed in immediate Isequence and therefore require stoppage or transfer of the stock being processed. For example, the use of printing masters in the form of glass plates or film with the image photographically carried thereon must be juxtaposed with respect to the lightsensitive coating or layer. Obviously, the material being processed at this stage cannot move continuously because of the need for orienting the photographic masters relative to the material or stock. With the instant invention, though, the material can be .moved continuously, thereby appreciably lreducing the fabrication time with a concomitant reduction in cost of the manufactured product.

Another object of the invention is to provide a method and apparatus that will not only process the stock on a continued basis, but which will afford accurate registry between patterns applied to opposite sides of the stock of material. More specifically, the pattern to be etched may be duplicated on both sides of the stock or portions of such patterns may be aligned depending upon what is desired as far as the etched design is concerned. If a wiring pattern is desired, metallic lands may be formed which will lie opposite each other; holes may be automatically formed in such lands if need be. In the case of a non-electrical pattern, such as a sieve, the holes or perforations to appear in the final etched product will be in registry with each other. Consequently, the invention obviates the need of positioning the photographically prepared masters heretofore employed and with respect to patterns applied to opposite of the material it is planned that the patterns be accurately aligned with each other even though on opposite sides; with the photographic masters that have been utilized, it has been exceedingly difficult to orient both masters properly in order to produce, say, precise alignment of holes that are to be etched through the metallic roll or other sheet stock. Consequently, the invention has for a specific aim the simultaneous etching from both sides of a metal strip with the assurance that holes Will be accurately tunneled together.

A further object of the invention is to provide a technique that will result in the forming of a well-defined pattern. Stated somewhat differently, conventional methods do not assure that a hole that is to be circular will possess an even edge therearound or that a metal strip constituting a wire or conductor will have a smooth edge imparted thereto. In other words, prior art methods have resulted in inferior results, producing irregular edges where smooth edges are desired or required. Thus, the accuracy of the pattern when practicing the present invention is improved.

Still another object is to provide a method and apparatus of the foregoing character that will per-mit the steps thereof to be performed in rapid sequence without the likelihood of contamination occurring. Actually, when utilizing photographic masters, such masters must be constantly checked for dirt and scratches; this is particularly true since they are moved about. Not only that, but the photographically prepared masters must be replaced from time to time which requires an expenditure of considerable sums of money and when in the form of glass plates, such plates are vulnerable to breakage, thereby further increasing the over-all costs. Not only does the present invention obviate the use of such photographic masters Ibut by resorting to a continuous process, there is little chance for dirt and other foreign matter to collect on the stock as it moves along which dirt or foreign matter would be apt to produce a reject as far as the iinal product is concerned.

Yet another object of the invention is to provide a method and apparatus in which the pattern or design can be readily changed. It is envisaged that cylindrical rolls or drums be utilized for applying an opaque substance in a prescribed manner and configuration to the photoresistive material on the metallic strip. The opaque pattern is applied by means of one or more rotatable cylinders having raised portions corresponding to the desired design or pattern on their cylindrical surfaces. All that need be done is to change the cylindrical roller with another one having a modified design thereon.

A still further object of the invention is to provide a pattern that can be virtually endless. Where electric circuits constitute the design, it will be manifest that there will be complete assurance that the electrical path will not be broken and that there need not `be any soldering of conductor ends together as is the case where the -process is stopped and started, this being the case in the abovealluded-to method utilizing photographic masters.

Quite briefly, my continuous etching process includes the washing and degreasing of a roll or strip metal, and then running the strip through a photoresist coater or applicator Whereat the photoresistive material flows on both sides of the strip to provide a light-sensitive layer. The photoresistive layer is then dried and the coated strip continues to a pattern-applying mechanism. The actual application of the pattern is in the form of linely divided carbon particles contained on one side of a plastic film. Where the design is to be applied to the photoresist material on both sides of the metal strip, then two such plastic lms will -be employed. A roller or drum is associated with each plastic lm so that it presses the desired design against the photoresistive layer, doing so by reason of raised portions thereon that are configured in accordance with the design or pattern that is to be subsequently etched into the metal strip. At this time, the photoresistive material must be hardened and this is done by passing the material between two are lamps, there being one on each side. As is conventional, the photoresistive layer is light-hardened yby reason of the light impingement thereon and where no carbon image has been formed, the regions are hardened due to the light striking these areas. The stock is now developed by passing through a bath of warm water. The water washes the carbon off and also the photoresistive material therebeneath which was shielded from the light. The stock is then advanced to what is termed a burning-in oven where the material is dried. The exposed metal surfaces `are now ready to etch, the hardened photoresistive material that remains protecting the other portions of the metal strip from the etchant.

These and other objects and advantages of my invention will more fully appear from the following description, made in connection with the accompanying drawings, wherein like reference characters refer to the same or similar parts throughout the several views and in which:

FIGURE 1 is a plan view rather diagrammatically portrayed showing exemplary apparatus for practicing my invention;

FIGURE 2 is a side elevational View corresponding to FIGURE l;

FIGURE 3 is a more pictorial side elevational view being for the purpose of showing the opaquing mechanism in greater detail and also the means via which the stock is advanced and the view therefore leaving out intermediate parts of the apparatus which include the exposure lamps and the developing station;

FIGURE 4 is a transverse sectional view taken in the direction of line 5-5 of FIGURE 3;

FIGURE 5 is a sectional view taken in the direction of line 4-4 of FIGURE 3;

FIGURE 6 is a perspective view of the opaquing mechanism with the top plate thereof removed;

FIGURE 7 is a top plan view looking down on the opaquing mechanism;

FIGURE 8 is a sectional view taken in the direction of line 8--8 of FIGURE 7;

FIGURE 9 is a sectional view taken in the direction of line 9-9 of FIGURE 8;

FIGURE 10 is a front elevational view corresponding to FIGURE 9 but with the stock and flanking carbon coated lms shown in section, and

FIGURE 11 is a greatly enlarged fragmentary view in section of the cylindrical rollers utilized for the purpose of impressing an opaque pattern onto the photoresistive layers on each side of the moving stock.

Referring rst to the diagrammatic FIGURES 1 and 2, it can be explained at the outset that the stock that has been selected for the purpose of illustrating the invention is in the form of a steel strip 10 that is oriented in a vertical plane. The strip 10, however, could be in the form of a laminate composed of metal foil but the assumption that the strip is of unitary structure is of benet in simplifying the ensuing description. The steel strip 10 is wound originally on a supply reel 12 and after processing is stored on a take-up reel 14 at the other end of the apparatus shown in these two ligures. The series of arrows 16 indicate the direction in which the stock moves.

Since it is contemplated that the entire method be of a continuous nature, it is necessary to clean the raw metal constituting the stock, more specifically the steel strip 10` in this instance, and to accomplish this the strip 10 is rst passed through a caustic tank labeled 18 having spray nozzles 20 arranged therein so as to bathe the metal as it progresses or advances through the tank. This degreases the strip 10 and then the caustic solution is removed at a wash station 22 having a number of H2O spray nozzles 24 located thereat.

Since the process is concerned with light-sensitive materials, it is necessary that certain portions of the over-all method be conducted in a darkened chamber (or under yellow or red light) and therefore a chamber 25 has been illustrated which contains adjacent the entrance thereof a photoresist coating applicator 26. The applicator 26 comprises a split nozzle 27 that directs photoresistive material downwardly so as to form a layer 28 on each side of the strip 10. The coated strip has been designated by the reference numeral 10a since it has been changed somewhat by reason of the addition of the layers 28 to each side of the strip 10 constituting the raw material or initial stock. The photoresistive layers 28 are dried in a drier 30 which consists of a relatively long oven 32.

An opaquing mechanism designated generally by the reference numeral 34 is utilized for the purpose of applying a desired design or pattern onto the dried photoresistive layers 28. Although the opaquing mechanism plays an important role in the practicing of the invention, the details thereof are best left for subsequent description. However, it can be pointed out at this stage that it is the purpose of the mechanism 34 to apply an opaque substance on the photoresistive layers 28, doing so only in certain areas or regions in order to form the pattern that will subsequently be etched into the steel strip 10.

It is from the opaquing mechanism 34 that the strip 10a advances to an exposure station 36 which includes a pair of arc lamps 38. The function of the arc lamps 38 is to harden the light-sensitive photoresistive material that is not covered or shielded by the opaque substance that is applied by the mechanism 34.

The next station is a developing station having a plurality of 'nozzles 41 that spray warm water onto the strip 10a. This causes the portions of the photoresistive layers 28 to be washed away where not hardened by the light. In other words, the opaquing that occurs at the mechanism 34 keeps those areas shielded by the opaque substance from becoming light hardened and this material is washed off at the developing station 40 with the consequence that exposed metallic surfaces are made available for etching. It is these surface areas that constitute the desired pattern or design that is to be etched. Before etching, though, the strip 10a is dried by passing it through an oven 42 generally similar to the oven 30, this oven being usually called a burning-in oven.

The actual etching occurs at the etching station 44 and hereagain a plurality yof nozzles 46 `are utilized for the purpose of spraying the strip 10a with the appropriate etchant. After etching, the strip 10a is subjected to washing at station 48 which then removes the hardened photoresistive material so that the strip 10a reverts to its original state as indicated by the reference numeral 10 but with the etched pattern having been added thereto.

The foregoing description has been `given largely to introduce the invention in a way that the details thereof can be better comprehended. Since the opaquing mechanism 34 is very important to a practicing of the invention, it will now be described. The mechanism 34 includes a base plate 52 and a top plate 54, the two plates serving mainly for the purpose of journaling a number of vertically disposed shafts. It will be noted that a pair of straightening rollers 56 are incorporated into the mechanism 34 and as their name indicates they function to straighten the strip a so that it will pass properly through the mechanism now being described. The rollers 56 are mounted on shafts 57.

Further included in the opaquing mechanism 34 are a pair of design applying cylindrical rollers or drums 58a and 5811. It will facilitate the ensuing description somewhat to assume that these rollers 58a, 5811 are intended to apply duplicate patterns to each side of the strip 10a. Also, it will help matters if We assume a very simple pattern and in this regard a multiplicity of small protuberances is formed on the cylindrical surfaces of these rollers. The protuberances are labeled 60 and since FIGURE l1 presents an enlarged view compared with the lother figures showing the strip 10a, attention is directed to FIGURE 11 for the purpose of showing the protuberances 60. These protuberances or raised portions are of circular shape and therefore will provide circularly configured holes when the strip 10a is subjected to etching at the station 44.

The cylindrical rollers 58a, 58h are mounted on vertical shafts 62a and 62b, respectively. The shaft 62a has attached thereto a gear 64a and the shaft 62h has similarly afiixed thereto a gear 64b, as best viiewed in FIGURE 9. Links 66a, 66h extend from the shafts 62a, 62b to additional shafts 68a and 68h. The additional shafts 68a and 68b have idler gears 70a and 70h in mesh with each other and also with the gears 64a and 64b. A connecting link 72 maintains the gears 70a and 70b` in their meshed relationshfip. Hence, when, say, the gear 64b is rotated, the gear 64a will be driven via the gears 70b and 70a so that it rotates in synchronism.

Since it is contemplated that the strip 10 will vary in thickness and also that the cylindrical rollers or drums 58a and 58b will conceivably be of different diameters when different patterns are required, it follows that it is highly desirable that some adjustment be made so that the shafts 62a and 62b on which the rollers are mounted can be adjusted. Such adjustment will, of courseJ control the amount of pressure that the rollers 58a, S8b apply to the strip 10a. To accomplish this goal, a pair of reciprocable actuating plates 76 are employed, there being one at the top and one at the bottom as can be seen in FIGURE 8. We will concentrate the description, however, on the upper such plate. The plate 76 is formed with a bearing hole 78 through which the shaft 62b projects, a slot 74 in the top plate 54 allowing the shaft to be moved toward or away from the strip 10a. Inasmuch as the cylindrical roller 58h is mounted on the shaft 62b, it will #be appreciated that the roller 58b iis moved relative tothe strip 10a in order to vary or adjust the pressural action thereagainst. From FIGURE 7, it will be discerned that a pair of parallel guides 80 are secured to the upper plate 54 and that these guides constrain the plate 76 so that it traverses a reciprocable path. In order to move the actuating plate 76 back and forth, still referring to the upper such plate, an upstanding flange 82 is provided at one end thereof and this flange 82 contains a collar or sleeve 84 by virtue of a knob 88, the shaft 86 can be rotated. The shaft 86 passes through a threaded support 90 which is ffixedly attached to the upper face of the topplate 54. Thus, the actuating plate 76 will be moved either toward or away from the strip 10a.

Another adjustment is desired with respect to the cylindrical roller 58h. Accordingly, several arcuate slots 92 are formed in the gear 64b. The gear 64b, in this way, can be angularly adjusted with respect to the roller 5817 and can be held fast by suitable screws 94. By means of gauging indicia 96 on the gear 64b and a reference marker 98 projecting upwardly from the cylindrical roller 58b, there being a slot 99 that allows the marker 98 to project through the gear 64b, an accurate angular adjustment in either direction as indicated by the arrow 100 can be obtained, the arrow 100 appearing in FIGURE l0. Stated somewhat differently, when looking down on the cylindrical roller 58h, this roller can be angularly oriented with respect to its companion roller 58a so as to bring the protuberances 60 into accurate alignment or registry at opposite sides of the strip 10a.

Another adjustment that is necessary in practice is a vertical one. To achieve this adjustment, a sleeve 102 is provided as shown in FIGURE l0, this sleeve having a vertical slot 104 therein. A screw 106 extends radially outwardly through the slot 104 and by tightening this screw against the shaft 62h which rotatably carries the roller 5812, the various protuberances 60 on this particular roller can be brought into vertical alignment with the protuberances 60 on the roller 58a. The vertical adjustment that is derived has been indicated by the arrow 108.

Describing now the manner in willich the strip 10a is moved longitudinally, it will be seen from FIGURES 3 and 4 that a drive motor 110 is coupled to a shaft 112 having several beveled gears 116, 118 and 120 thereon. A beveled gear 122 is fixed to the lower end of one of the shafts 57 and through the agency of a pair of meshed pinions 124 on the two shafts 57, both of the straightening rollers 56 are rotated, thereby imparting some driving action to the strip 10a. Additional driving action is transmitted to the strip 10a via still another beveled gear 126, this last-mentioned beveled gear being secured to the lower end of the shaft 62a. Rotation of the roller or drum 58h having the raised pattern thereon will cause the other roller or drum 58a to be rotated through the gear train comprised of the gears 64b, 7011, 70a and 64a. The third beveled gear on the shaft 112 is engaged with a beveled gear 128 affixed to the lower end of one of two vertically disposed shafts 130 having pinions 132 mounted thereon. The shafts 130 carry drive rolls 134 that act against the sides of the stnip 10a so as to supply most of the moving force to the `strip 10a. It is important that the strip not become buckled and the synchronized drive via the shaft 112 that has just been described assures that the strip 10a is not inadvertently flexed or bowed. While no motor is needed for the supply reel 12, there is a need for rotating the take-up reel 14 and while the shaft 112 could be extended, it simplifies matters to show a motor 136 in FIG- URE 2 which acts through a slip clutch 138 to roll the strip 10 onto the reel 14, this being after the strip has been etched and the layers 142 completely removed at the station 48.

Passing now to a description of how the pattern carried on the rollers or drums 58a, 58b is transferred to the strip 10a, it will be observed that a set of two plastic films 140, there being one for each roller 58a and 58h, are passed between the rollers 58a, 58h and the opposite sides of the strip 10a. The films 140 should be as pliable as possible and also as thin as possible. Accordingly, 0.0005 inch Mylar (polyethylene terephthalate) or Tedlar (polyvinylfluoride) are very satisfactory. Not only are these particular plastic films sufiiciently flexible and deformable so that the raised portions 60 constituting the pattern or design can be applied to the strip 10a but such plastic material accepts very readily a coating 142 of finely divided carbon powder or particles. The raised portions 60 are instrumental in bearing against the uncoated sides of the films 140 and press the carbon coated sides against the photoresist layers 28 that have been applied to the original metal strip 10, Consequently, portions of the coating 142 are transferred from the films 140 to the photoresistive layers 28. Stated in somewhat broader language, an opaque substance, in the form of finely divided carbon particles, is pressed against the layers 28 by reason of the protuberances 60 constituting the pattern image and the opaque substance darkens the areas or regions that constitute the pattern or design that is to be etched into the metal strip 10. A pair of supply spools 144 have :the carbon-coated plastic film strips carried thereon and the material is withdrawn past the rollers 58a, 58b and is then wound on a pair'of take-up spools 146. For simplicity of discussion, it can be assumed that a pair of drive motors 148, there being one for each spool 146, are employer for rotating the take-up spools. Since the films 140 must be moved in Synchronism with the movement of the strip 10a, a slip clutch 150 is located between each drive motor 148 7and its respective take-up spool 146. It is important to understand, though, that there should be no relative movement of the films 140 with respect to the strip 10a. In other words, the film 140 in each instance is precisely synchronized as far as its tangential movement when bearing against the strip 10a with the movement of such strip.

Having mentioned the application of an opaque pattern, the reference numeral 152 is collectively used to designate such a pattern and the opaque pattern appears in FIGURES 6 and 1l. Owing to the scale of FIGURE 1l, it will be perceived from lclose inspection thereof that the protuberances 60 in transferring carbon particles to form the pattern 152 have formed indentations or recesses 154, the carbon particles actually being at the bottom or base of each recess. The peripheral edge of each recess 154 becomes compacted by virtue of the raised portions or protuberances 60 and this is a highly beneficial result in practicing the teachings of the present invention. When forming holes, as we have considered the pattern or design that is desired to constitute, the compaction that takes place around the edge of each recess 154 will keep the photoresistive material from fiaking olf or becoming inadvertently dislodged. Consequently, a well-defined pattern structure is provided which will in the etched product allow accurately dimensioned holes to be made in the basic stock or metal strip 10.

From the foregoing, it is thought that the method and apparatus constituting my invention can readily be comprehended. However, a brief description outlining the procedural steps will undoubtedly be of help in appreciating the benefits to be derived from a practicing of the invention. With the motors 110, 136 and 148 operating, the strip 10 will be withdrawn yfrom the supply reel 12. After being degreased and washed at the stations 18 and 22, the strip enters the chamber 25. Although the chamber 25 has been depicted as a structural enclosure, it will be appreciated that this may amount to only a yellow light region. At any rate, the photoresistive material 28 is applied at the station 26. The photoresistive material 28 is commercially available and can be a material composed of ammonium dichromate, sulfuric acid, distilled water and photoengravers glue. The amount of sulfuric acid can be increased somewhat over what is usually used in order to improve the ability of the layers 28 as far as the reception of the carbon particles thereon. Of course, as more fully described hereinbefore, the carbon particles constituting the pattern 152 are applied by the opaquing mechanism 34. It has been explained that the plastic films 140 have one side thereof coated with finely divided carbon particles in the form of the coating 142. Sufficient carbon particles are transferred to the photoresistive layers 28 so as to darken the recesses 154 and'thus form the pattern labeled 152. The exposure station 36 hardens the regions that have not been darkened and thus only the areas underlying the pattern 152 will remain soft. The developing station 40 removes the carbon and the underlying unhardened resist material, thereby leaving metal areas on the strip 10 exposed. Such exposing of the metal areas allows these areas to be etched at the etching station 44 after drying in the oven 42. Inasmuch as steel has been selected for the purpose of exemplifying the invention, a suitable etchant in the form of iron chloride can be sprayed onto the exposed metallic surfaces at the station 44. After all the remaining resistive material which has been hardened after the station 36 is removed, the

completed etched strip will be coiled on the take-up reel 14.

Those familiar with prior art procedures will appreciate the fact that the so-called vacuum frame previously utilized in connection with the employment of the photographic plates constituting the masters that had to be adjusted within the frame is Acompletely eliminated when practicing the present invention. The positioning of the photographic plates had to be done with extreme care, particularly when two such masters had to be aligned at opposite sides of the stock being processed. Obviously, such a procedure required an intermittent operation whereas the present invention results in a continuous processing of the stock. Also, the handling of the master plates in the past resulted in their wear and an accompaying need for replacing them from time to time. Since the present method and apparatus involves a continuous processing of the stock, there is an accelerated production of the etched pattern without causing rejects. On top of this, extremely accurate patterns can be produced. The accuracy stems from both the well-dened opaque areas that can be applied to the photoresistive material plus the compaction that occurs and in addition the elimination of the photographic master plates also precludes stray light from striking portions of the resistive material that should not become hardened. Not only are these attributes derived as far as an enchanced end product is concerned, but the end result is obtained very inexpensively. Still further, the particular design can be changed very easily inasmuch as it is only required that the different rollers or drums 58a, 58b be substituted.

It will, of course, be understood that various changes may be made in the form, details, arrangements and proportions of the parts without departing from the scope of my invention as set forth in the appended claims.

I claim:

1. In a system for etching a desired pattern in a continuously longitudinally moving metal strip having a photoresistive layer on one side thereof, a method for preparing the metal strip for etching, comprising the steps of:

(a) placing a surface containing a transferable opaque substance on its face adjacent the metal strip facing the photoresistive layer;

(b) moving said surface at the same velocity as the metal strip; and

(c) momentarily pressing portions of the surface faceto-face against the strip while both are moving to cause said portions of the opaque substance to adhere to the photoresistive layer to form a darkened coating pattern corresponding to the pattern to be etched.

2. The method as in claim 1 wherein the surface of transferable opaque substance is a carrier strip of compressible plastic film having a coating of finely divided carbon particles, said particles characterized by adhering securely to the photoresistive layer when pressed firmly thereagainst.

3. The method as in claim 2 wherein the carbon-particle coating is momentarily pressed against the metal strip by a cylindrical roller containing raised surface areas making rolling contact with the uncoated side of said plastic film.

4. The method as in claim 3 wherein the metal sheet contains photoresistive coatings on both sides and the method for preparing the metal strip for etching includes: applying process steps (a), (b) and (c) to both sides of the metal strip concurrently.

5. In a system for etching a desired pattern through a continuously longitudinally moving metal strip from both side of the strip, said strip having photoresistive layers on both sides thereof, a method for preparing the metal strip for two sided etching, comprising the steps of:

(a) placing surfaces containing a transferable opaque substance on their faces adjacent the metal strip on opposite sides of said strip facing the photoresistive layers;

(b) moving said surfaces at the same velocity as the metal strip;

(c) applying identical patterns of said opaque substance to the opposite faces of the metal strip by pressing said substances-bearing surfaces at least momentarily against the respective photoresistive layers directly opposite one another in register while the surfaces and the strip are so moving with suicient pressure to cause at least selective portions of the opaque substance to adhere securely to the respective photoresistive layers 6. The method as in claim 5 wherein the surfaces of transferably opaque substances comprises carrier strips of compressible plastic film each having a coating of finely divided carbon particles, said particles characterized by `adhering securely to the photoresistive layer when pressed rrnly thereagainst.

7. The method as in claim 6 wherein the opaque substance surfaces are placed into momentary pressing contact with the metal strip by feeding the continuously mov- References Cited UNITED STATES PATENTS 2,206,290 7/ 1940 Meyer 156-10 2,762,149 9/1956 Mears 156--345 2,881,073 4/ 1959 Maclay 96-36 JACOB H. STEINBERG, Primary Examiner.

U.S. C1. X.R.

156-3, 10, 11; 96-36, 36.2; lOl-2.44, 229, 332, 336; 118-211, 212, 227 

